The present invention relates to a method for determining the rail pressure of an injector including a voltage-controlled piezoelectrical actuator.
Conventionally, in an injector including a piezoelectrical actuator, the motion of the nozzle needle is not driven directly but via a hydraulic coupler. One task of the coupler is to reinforce the stroke of a control valve. For correct functioning, however, the hydraulic coupler must be completely charged, especially since in every driving of the piezoelectrical actuator a portion of the fluid is squeezed out of the hydraulic coupler through leakage gaps. In this context, the recharging occurs in the pause between two injections. In order to release a predetermined quantity of fluid in the high-pressure channel, it is necessary to know the pressure in the high-pressure channel. This pressure may be measured by an appropriate sensor, which is arranged in the high-pressure line system (common rail system) at an appropriate location. In this context, the problem may arise that an erroneous rail pressure measurement may result from the failure of the pressure sensor. Due to the incorrect rail pressure measurement, it is then no longer assured that the predetermined injection quantity will actually be released. This may be critical especially in a motor-vehicle including an internal combustion engine, if the predetermined quantity of fuel is not injected. The result may be abrupt disruptions in functioning and potentially the shutdown of the internal combustion engine. Furthermore, undesirable, large injection quantities may also occur.
In contrast, the method according to the present invention for determining the rail pressure of an injector including a voltage-controlled piezoelectrical actuator may provide the advantage that the pressure in the high-pressure channel of the injector is measured by measuring the induced piezovoltage. The result is a redundant pressure measurement, which makes it possible to monitor the measured value of the pressure sensor.
It may be advantageous that, using an algorithm, for example, in the form of a linear equation or a table, it is possible to reach conclusions regarding the prevailing rail pressure on the basis of the measured piezovoltage. In this manner, it is possible to obtain an electrical characteristic quantity that is assigned to the rail pressure and that may easily be further processed by the electronics.
By comparing the calculated rail pressure with the measured value of the pressure sensor, it is possible, in a manner, to monitor the normal functioning of the pressure sensor. If the pressure sensor fails, for example, as a result of a line break or a fault, then the redundant measured value may be retrieved for emergency operation in maintaining the functioning of the internal combustion engine.
In the case of a fault, it may be advantageous to store the measured voltage values or the pressure value, so that the event may be reconstructed at a later time point. This may be especially important for an internal combustion engine that includes a common rail injection system, to assure operating reliability.
An example embodiment of the present invention is illustrated in the drawings and is discussed in greater detail in the description below.